Ldmos device with isolation guard rings

Abstract

A method of forming a LDMOS semiconductor device and structure for same. A preferred embodiment comprises forming a first guard ring around and proximate the drain of a LDMOS device, and forming a second guard ring around the first guard ring. The first guard ring comprises a P+ base guard ring, and the second guard ring comprises an N+ collector guard ring formed in a deep N-well, in one embodiment. The first guard ring and second guard ring prevent leakage current from flowing from the drain of the LDMOS device to the substrate.

Description

TECHNICAL FIELD [0001] The present invention relates generally to semiconductor devices, and more particularly to a lateral double-diffused metal oxide semiconductor (LDMOS) device and method of manufacture thereof. BACKGROUND [0002] An LDMOS device is basically a metal oxide semiconductor field effect transistor (MOSFET) fabricated using a double-diffusion process with coplanar drain and source regions. A prior art LDMOS device 100 is shown in a cross-sectional view in FIG. 1. An N+ buried layer 104 of silicon is formed within the top portion of a P-substrate 102. A high voltage P well (HVPW) 108 extends downwardly from the top surface of the substrate 102. The HVPW 108 includes an N+ source 110 having a distance L from the junction between an adjacent high voltage N well (HVNW) 106 and the N+ source 110, wherein distance L defines the channel of the device 100. A gate 112 is formed proximate the source 110 over a field oxide (FOX). The LDMOS device 100 includes a drain 114 compris...

AI Technical Summary

Benefits of technology

The present invention provides a design for an LDMOS device that prevents leakage current and solves reliability issues. The device includes a first and second guard ring that act as an NPN parasitic transistor to isolate the drain from the substrate. The device also allows for simultaneous doping of the drain and the first and second high voltage well regions, and the formation of a deep well region within the first guard ring. The technical effects of the invention include improved current isolation, prevention of leakage current, and improved reliability of the LDMOS device.

Problems solved by technology

A problem with the prior art LDMOS device 100 shown in FIG. 1 is that if the LDMOS device 100 is connected to an inductor load, such as to drive a digital versatile disc (DVD), a transient negative voltage may be fed back at the drain 114 when the power is off.

The transient negative voltage can create leakage current.

This leakage IL degrades device performance, causing a latch-up effect, early breakdown, and reliability issues for the LDMOS device 100, as examples.

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